1. Field of the Invention
The present invention relates to an exposure apparatus, a control method thereof, and an image forming apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus, image forming is performed by forming an electrostatic latent image by an exposure apparatus irradiating light on a photosensitive drum, developing the electrostatic latent image with a development apparatus, and transferring a resulting developer image to a recording material or the like. The exposure apparatus is ordinarily provided with a laser light source that emits laser light, and a laser control apparatus that controls the laser light source. Among electrophotographic image forming apparatuses, there are image forming apparatuses that employ a laser light source having a plurality of light-emitting points (laser elements). The laser control apparatus controls the laser light source in a data light-emitting mode in which the laser light source is caused to emit light corresponding to an image signal, an APC (Auto Power Control) mode in which the strength of the laser light source is kept at a fixed level, or a non-emitting mode in which the laser light source is not caused to emit light. Japanese Patent Laid-Open No. 2004-284185 proposes technology whereby a sequence of control of a light amount of a plurality of laser elements is stored in advance, and the light-emitting point whose light amount is controlled is switched according to a switching signal that is input from outside.
However, in the above conventional technology, there are the problems described below. For example, when the above laser control apparatus is used with a plurality of such laser control apparatuses disposed in a line, the effects of noise from outside may sometimes cause a malfunction. Among image forming apparatuses, there are a plurality of models having different print speeds. For example, print speed is high in the case of an image forming apparatus for commercial printing designed for high-volume printing, and on the other hand print speed is low in the case of an image forming apparatus for small offices designed with an emphasis on conserving space.
Ordinarily, as the number of light sources provided in a laser element increases, a greater number of scan lines can be formed in a sub-scanning direction (rotational direction of a photosensitive drum) in a single scan, so increased speed of the image forming apparatus can be realized. Therefore, in an image forming apparatus having a high print speed, a laser element having a large number of light sources is used, while in an image forming apparatus having a low print speed, a laser element having a smaller number of light sources is used.
On the other hand, regarding the laser control apparatus that controls the laser element, in order to increase general applicability, one laser control apparatus is used for a laser element having a small number of light sources, and a plurality of laser control apparatuses disposed in a line are used for a laser element having a large number of light sources. In the case of a configuration in which a plurality of laser control apparatuses disposed in a line are used, it is necessary to pay attention to the combination of control states of the respective laser control apparatuses. For example, while one laser control apparatus is in an APC control mode, it is necessary for other laser control apparatuses to be in an OFF state. The reason for this is that since there is only one PD (photodetector) for a plurality of light-emitting points, when performing APC control, it is necessary to perform control such that only laser light of the light-emitting point subject to APC control is incident on the PD.
However, according to the conventional technology, there is the problem that when noise is included in a light amount switching signal that is input to one laser control apparatus, the control procedures of the laser control apparatuses do not transition at an intended timing relative to each other, so a malfunction occurs in an image forming operation. For example, a situation also occurs in which two laser control apparatuses are simultaneously in the APC control mode. Here, there is the problem that APC control is not properly performed, so it is not possible to suppress degradation of a laser element.